1. Field of the Invention
The present invention relates to a semiconductor device including a ferroelectric capacitor and suited to a nonvolatile memory or the like, and a method of fabricating the semiconductor device.
2. Description of the Related Art
A ferroelectric material is applied to a memory (semiconductor memory), actuator, sensor, and the like since the material has high ferroelectricity, piezoelectricity, and pyroelectricity. As for a memory, this material is applicable to a nonvolatile memory by using the hysteresis of ferroelectricity. These semiconductor devices use a capacitor structure made up of a lower electrode, ferroelectric film, and upper electrode stacked in this order on a lower layer. As the ferroelectric film, Pb(Zr, Ti)O3 (to be also referred to as PZT hereinafter) having higher ferroelectricity than other ferroelectric materials is mainly used. As a method of forming this ferroelectric film, a sol-gel method, sputtering, CVD (Chemical Vapor Deposition), or the like is used.
When a thin PZT film is formed using sputtering or CVD, however, the initial nucleation density of PZT on a lower layer is low, and this produces variations in grain size. As a countermeasure against this problem, a method is reported in, e.g., “Jpn. J. Applied. Phys., Vol. 32, No. 9B, pp. 4086-4088 (1993)”. In this method, an initial layer of PbTiO3 is formed on an electrode in advance, and a PZT film is formed after that.
Unfortunately, even when the initial layer of PbTiO3 is formed as in the above conventional film formation method, it is impossible to well control the alignment of a PZT film formed on this initial layer. If this alignment is low, high remanent polarization is difficult to obtain, so no high reliability can be obtained.